High integration and miniaturization of semiconductor devices are advancing year after year in an accelerated manner. Currently, a pattern with a line width of about 45 nm is being formed by excimer exposure. However, nowadays, in accordance with the advance in the miniaturization of semiconductor devices, there is a demand for pattern formation with a line width of 32 nm or less. Fine processing for such pattern formation is difficult to be handled by the conventional excimer exposure. Therefore, use of shorter wavelength Extreme Ultra Violet (EUV) as the exposure light is being under consideration.
EUV has a property of being easily absorbed by every substance. Therefore, in an EUV lithography method, exposure is conducted in a catoptric system. Specifically, light exposure of a resist is performed by EUV reflected by an original plate having an exposure pattern reflected thereon. During such exposure, when foreign matters are attached to the original plate, exposure of a desired pattern becomes difficult due to EUV absorption or scattering by the foreign matters. Therefore, protection of the EUV irradiation surface of the original plate with a pellicle has been taken into consideration.
In addition, in the EUV lithography, contamination of an exposure device by scattering particles (debris) generated by the EUV light source. When the scattering particles (debris) are attached to an optical system, or scrape the EUV reflection surface, the efficiency of EUV irradiation becomes lowered. Further, when the scattering particles (debris) are attached to the original plate, as described above, the resist cannot be exposed in a desired pattern. Therefore, placement of a filter window in the EUV irradiation device, the filter window being a trap for the scattering particles (debris), has been taken into consideration.
The above-mentioned pellicle membrane and filter window are required to have (1) high transmittance of the EUV, and (2) resistance against decomposition/deformation by the EUV irradiation. As the pellicle membrane or filter that satisfies such requirements, a membrane composed of a monocrystalline silicon (PTLs 1 and 2), an aluminum nitride film laminated on a metal mesh (PTL 3), a graphene film (PTL 4), and the like are proposed.